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UCC2888 Datasheet(PDF) 1 Page - Texas Instruments |
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UCC2888 Datasheet(HTML) 1 Page - Texas Instruments |
1 / 6 page Off-line Power Supply Controller • Transformerless Off-line Power Supply • Wide 100VDC to 400VDC Allowable Input Range • Fixed 5VDC or Adjustable Low Voltage Output • Output Sinks 200mA, Sources 150mA Into a MOSFET Gate • Uses Low Cost SMD Inductors • Short Circuit Protected • Optional Isolation Capability The UCC3888 controller is optimized for use as an off-line, low power, low voltage, regulated bias supply. The unique circuit topology utilized in this device can be visualized as two cascaded flyback converters, each operating in the discontinu- ous mode, both driven from a single external power switch. The significant benefit of this approach is the ability to achieve voltage conversion ratios as high as 400V to 2.7V with no transformer and low internal losses. The control algorithm utilized by the UCC3888 sets the switch on time inversely proportional to the input line voltage and sets the switch off time inversely propor- tional to the output voltage. This action is automatically controlled by an internal feedback loop and reference. The cascaded configuration allows a voltage conver- sion from 400V to 2.7V to be achieved with a switch duty cycle of 7.6%. This topol- ogy also offers inherent short circuit protection since as the output voltage falls to zero, the switch off time approaches infinity. The output voltage is set internally to 5V. It can be programmed for other output voltages with two external resistors. An isolated version can be achieved with this topology as described further in Unitrode Application Note U-149. UCC1888 UCC2888 UCC3888 3/97 FEATURES DESCRIPTION OPERATION With reference to the application diagram below, when input voltage is first applied, the current through RON into TON is directed to VCC where it charges the external capacitor, C3, connected to VCC. As voltage builds on VCC, an internal undervol- tage lockout holds the circuit off and the output at DRIVE low until VCC reaches 8.4V. At this time, DRIVE goes high turning on the power switch, Q1, and redirect- ing the current into TON to the timing capacitor, CT. CT charges to a fixed threshold with a current ICHG=0.8 • (VIN - 4.5V)/RON. Since DRIVE will only be high for as long as CT charges, the power switch on time will be inversely proportional to line voltage. This provides a constant (line voltage) • (switch on time) product. Note: This device incorporates patented technology used under license from Lambda Electronics, Inc. TYPICAL APPLICATION UDG-96013 |
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